Modern photon radiotherapy effectively spares cardiac structures more than previous volumetric approaches. Still, it is related to non-negligible cardiac toxicity due to the low-dose bath of surrounding normal tissues. However, the dosimetric advantages of particle radiotherapy make it apromising treatment for para- and intra-cardiac tumours. In the current short report, we evaluate the cardiac safety profile of carbon ion radiotherapy (CIRT) for radioresistant intra- and para-cardiac malignancies in areal-world setting. We retrospectively analysed serum biomarkers (TnI, CRP and NT-proBNP), echocardiographic, and both 12-lead and 24-hour Holter electrocardiogram (ECG) data of consecutive patients with radioresistant intra- and para-cardiac tumours irradiated with CIRT between June 2019 and September 2022. In the CIRT planning optimization process, to minimize the delivered doses, we contoured and gave ahigh priority to the cardiac substructures. Weekly re-evaluative 4D computed tomography scans were carried out throughout the treatment. Atotal of 16patients with intra- and para-cardiac localizations of radioresistant tumours were treated up to atotal dose of 70.4 Gy relative biological effectiveness (RBE) and amean heart dose of 2.41 Gy(RBE). We did not record any significant variation of the analysed serum biomarkers after CIRT nor significant changes of echocardiographic features, biventricular strain, or 12-lead and 24-hour Holter ECG parameters during 6months of follow-up. Our pilot study suggests that carbon ion radiotherapy is apromising radiation technique capable of sparing off-target side effects at the cardiac level. Alarger cohort, long-term follow-up and further prospective studies are needed to confirm these findings.